1. Field of the Invention
The present invention relates to signal modulation devices and signal amplifiers cooperative therewith, and more particularly, to a signal modulation device and a signal amplifier cooperative therewith for use in a wireless RFID tag reader.
2. Description of Related Art
Radio-frequency identification (RFID) system relates to an automatic identification technology that involves affixing a small electronic tag to a product which is to be checked and monitored by a device known as “reader” which in turn transmits the data stored in the electronic tag back to the system via a wireless RF means, thus achieving remote authentication, tracking, control, management and handling.
The electronic tags come in two general varieties, passive or active. In particular, passive RFID tags have no internal power supply. The minute electrical current induced in the antenna by the incoming radio-frequency (RF) signal provides just enough power for the CMOS integrated circuit in the tag to power up and transmit a response.
The amplitude shift keying (ASK) modulation is a form of modulation that represents digital data as variations in the amplitude of a carrier wave, which is adopted to modulate the above-mentioned RF signal. Hence, signal modulation circuit is often designed on RFID tag reader to convert the information to be transmitted to ASK signal, which is in turn transmitted to the RFID tag.
Referring to FIG. 1, a schematic of the ASK modulation circuit is illustrated, the modulation circuit includes a D/A converter, a frequency synthesizer, bandpass filters, mixers and a power amplifier.
However, due to characteristics of ASK modulation signal, an ASK modulation circuit design does not require a D/A converter to generate a precise ASK signal. Moreover, adding a D/A converter to the baseband I/O terminals will significantly increase the overall power consumption of the RF circuit as well as the chip area.
In summary, it has become an urgent issue to designers of the RF circuit design field to propose a circuit that decreases the design complexity of the conventional ASK modulation circuit having a D/A converter, so as to significantly reduce the overall power consumption of the RF circuit as well as the chip area.